Bloodstain Pattern Analysis: is the examination of the shapes,

locations, and distribution of patterns of bloodstains, in order to provide

an interpretation of the physical events that gave rise to their origin.

The following Information may be obtained from a

proper Bloodstain Pattern Analysis:

1. Distance from the blood source to the target

2. Direction of travel and impact angles

3. Nature of the force used to cause the bloodshed

4. The object used to cause the bloodshed

5. Sequencing of multiple bloodshed events

6.Interpretation of contact or transfer patterns

When properly documented, bloodstain patterns found at the crime scene, or on a particular person's clothing, can be used to:

  1. 1.Confirm or refute the position of a victim, witness, suspect, or defendant

2. Determine if there is evidence of a struggle, or if the assault is "one sided"

3. Confirm or refute statements made by principles in the case:

                IE: Are stain patterns on a particular person's clothing consistent

                     with accounts given by the victim, witness, or defendant?

Blood Flight Characteristics:

Blood will not break up unless it is acted upon by force. The force must be great enough to overcome the surface tension of the blood

Blood forms a spherical shape (perfect circular shape) almost immediately upon separating from the blood source. The spherical shape is caused by the surface tension of the blood.

Surface Tension causes the blood drop to pull itself in; both horizontally and vertically.

The blood drop will settle into a spherical shape, as a result of the surface tension.

The surface tension will maintain the sphere shape of the blood drop until it impacts with the


SPATTER VS TRANSFER: The simplest type of blood spatter analysis is determining spatters from transfers.

    Spatters are created when blood is acted upon by force, and travels through the air before landing on a    

    target surface.

    Transfers occur when a blood source comes in direct contact with a target surface area.

Transfer - Swipe Pattern

Transfer - Wipe Pattern

Spatter Pattern


  1. Bloodstains can occur on a variety of surfaces. The type of
    surface that free falling blood strikes affects the
    appearance of the resulting spatter.

  2. Blood drops on a smooth surface will make a more uniform
    or regular circular shape.

  3. Blood drops on a rough surface will make an irregular
    shaped stain with rough or jagged edges.


  1. Blood that falls at the speed or force of normal gravity

  1. These spatters usually fall from an open wound, or from a
    surface that is saturated with blood

  1. The majority of the Low Force Impact Spatters are large,
    circular, spatters with diameters of 4mm or more

  1. Low Force Impact Spatters will increase in size as the
    distance fallen increases, however, the size of the spatters
    will remain constant after approx 4 feet


  1. Produced with more energy or force than gravity

  1. The force of the impact causes the blood to break into
    smaller size spatters  relative to the amount of  force applied

  1. This type of spatter is usually seen in blunt force, stabbings,
    and secondary spatters

  1. Produced when the majority of larger drops of blood are
    broken into smaller spatters with diameters of 2 – 4 mm

  1. The force associated with this type of spatter is greater than
    25 ft per second   


  1. Impact spatter that measures less than 2mm in

  2. The force necessary to produce this size spatter
    is greater than 100 ft per second

  3. This type of spatter is usually associated with
    gunshots, explosions, and high speed collisions

  4. High Force Impact Spatter takes on a "mist like"

IMPACT SPATTERS: are a random pattern of spatter of varying sizes

It is important to note that the term "Velocity" does not measure the speed at which the blood is traveling, but rather is used to describe or measure amount of force applied to the blood, to cause it to spatter.

Angle of Impact:  

The steeper the impact, the more

elliptical or elongated, the blood drop


The "tail" points to the direction of

the blood drop

Angle of Impact


  1. Measure the width and the length of the stain/spatter                                        

                                              sine=  width    =   9mm             

                                                         length   =  18mm

  1. 9 divided by 18 = 0.500

  2. Arcsine 0.500 = 30 degree angle of impact

  1. Do not measure the “tail”

            • it is a secondary force or event.

  1. Divide the smaller number by the larger number


  1. When a bullet strikes a target, some high force impact spatter may be directed back toward the gun that fired the shot. This is known as "back spatter"  

  1. If the bullet exits its target, a larger
    amount of high force impact spatter may be directed in the same direction as the bullet. This is known as "forward spatter".

The amount of high force impact spatter created will depend upon the size or caliber of the bullet fired, as well as the distance from the gun to the target. The larger the bullet, or projectile, the greater

the spatter. The closer to the target that the gun is fired...the great the spatter.

For a complete list of bloodstain pattern terms, as recommended by the Internation Association of Blood Stain Pattern Analysts. (IABPA), go to: These terms should serve as a guide, for those who work and teach in the field of Blood Stain Pattern Analysis. These terms are not meant to be all encompassing

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